382 Knight . — Further Observations on the Transpiration , 
Table VII. 
Summary of experiments on various species to determine changes of 
water-content through the day. 
Time of 
Time of 
No. of 
compari- 
Experi- 
ment No. 
Species. 
first 
determina- 
second 
determina- 
Change in water -content. 
tion. 
tion. 
Average. 
Max. 
Min. 
sons. 
83 
Eupatorium 
8.0 a.m. 
2.0 p.m. 
-0.25 
-1.8 
+ 0.7 
6 
86 
adenophorum 
— o-6 
99 
9*° >» 
2.0 „ 
— 1. 1 
— 
6 
88 
99 
0° 
0 
1.0 „ 
-0.5 
-i*3 
+ i*3 
12 
88 
99 
1. 15 p.m. 
5-15 „ 
+ 0.4 
+ 1-0 
-0.4 
12 
9 [ 
Peristrophe 
8.30 a.m. 
I - I 5 „ 
— 0.2 
— o*6 
+ 0.2 
8 
speciosa 
93 
Cycas circinalis 
8-45 >, 
1-30 £ 
— 0.1 
-0.4 
+ o-6 
6 
94 
Peristrophe 
ii- 3° » 
4^5 » 
+ 0-1 
— 
— 
6 
speciosa 
+ 0.6 
109 
Quince 
1 0.0 „ 
3-30 „ 
+ 0.4 + o-i 
+ 0.1 
6 
1 10 
Apple 
3.30 p.m. 
9.30 a.m. 
— O-I 
— 
— 
40 
107 
Fraxinus 
10.0 a.m. 
3.30 p.m. 
-4.4 1 
-7.0 
-3*o 
8 
108 
9 9 
9° » 
4.0 „ 
~ i*4 1 
-2.9 
+ 1.3 
20 
The writer does not offer any complete explanation of these differences, 
but suggests that the wide divergence between the habitats of the plants 
used by Livingston and Brown and of those in the present investigation 
may account for the difference in behaviour. It is evident that a plant 
which can suffer a decrease in water-content of 8 per cent, without becoming 
flaccid is more fitted to flourish in the extreme conditions of a desert habitat 
than one which loses its turgidity if its leaf water falls from 85 per cent, to 83 
per cent. 
Summary. 
It has been demonstrated by simultaneous observations that an increase 
of transpiration rate accompanies the stomatal opening which occurs during 
the early stages of wilting. 
There is no correlation between the temperature of the air in which 
wilting occurs (i.e. presumably the rate of wilting) and the magnitude of 
the accompanying increase in transpiration rate or the magnitude of the 
increase of stomatal aperture. 
The time elapsing between the commencement of wilting and the 
attainment of the maxima of transpiration rate and stomatal aperture is 
dependent on the rate of wilting. Thus the attainment of these maxima 
represents definite stages of the wilting process. 
These stages are reached very early in the process, before the water- 
content of the wilting leaf has decreased more than about 1 per cent. 
1 These shoots were intentionally allowed to wilt between the early and the later determinations 
to obtain an indication of the magnitude of the water loss corresponding with visible wilting. In 
the notes of these experiments the leaves in No. 107 are described as ‘badly wilted’, and those in 
No. 108 as ‘slightly wilted’. 
